How to use the @nakedobjects/restful-objects.withUndefined function in @nakedobjects/restful-objects

setCopyViewModel(dvm: IDraggableViewModel | null) {
        this.copiedViewModel = dvm;
        this.copiedViewModelSource.next(Ro.withUndefined(dvm));
    }

setDateIfChanged(newDate: momentNs.Moment) {
        const currentDate = this.dateModel;
        if (!newDate.isSame(Ro.withUndefined(currentDate))) {
            this.setValue(newDate);
            setTimeout(() => this.model = this.formatDate(this.dateModel));
        }
    }

setTimeIfChanged(newTime: momentNs.Moment) {
        if (!newTime.isSame(Ro.withUndefined(this.time))) {
            this.time = newTime;
            setTimeout(() => this.model = newTime.format('HH:mm'));
        }
    }